walking skeletons and world breakers
by sceera1
Summary: sans has been defeated by the human and just as they're about to die, he shortcuts through the barrier. he ends up landing on the dead couch of our favorite skeleton detective. don't worry, sans will live. FIRST SKULDUGGERY UNDERTALE CROSSOVER! yay to me! i do not own the image, undertale or SP. rights to respective owners.
1. Chapter 1

**this is an idea that kept on coming back. it may or may not be good, i don't know so don't hate me for how bad it might be. on with the story.**

 _Damn, this hurts._ Sans thought, as blood seeped through his jacket. it easily soaked through and formed a puddle on the golden floor of the judgement hall. he stared at the human for moment, then at himself, then back at the human. **"** **so..."** he muttered weakly, spitting blood. **"** **guess that's it, huh?"** he felt himself falling into unconsciousness. the blood loss was already taking its toll. **"** **just...don't say i didn't warn you."** he silently thought to himself, _after the reset, don't expect me to come running as Undyne rips you limb from limb, while you attempt to make up for everything you've done._ he closed his eyes and shakily got to his feet. he truly relaxed for the first time since he first saw the human in this time-line. **"whelp,"** he said in his patented joking pose. **"i'm going to Grillby's."** he slowly shifted out of the human's view and tried to shortcut. there was a loud CRACK and a rush of wind and he collapsed onto a couch that was very sorry for its existence. he thought he saw a tall skeleton standing not too far away from him and said, **"** **P** **apyrus, do you want anything?"** before passing out.

 _-LINE BREAK-_

Skulduggery just got back to his house after solving a murder case. the murderer had the power to kill using a heart attack but, somehow, it didn't affect things that had already died. the killer also like to hide the cause of death on is victims by using a knife to shred their insides. this is what lead to the killer's capture. luckily for Skulduggery he was already dead and somehow Valkyrie's revival from being just a soul and returning to their body, counted as dying and coming back. he had dropped off Valkyrie back at home, straight to their house, mind you, and not leaving them at the pier to walk home since her parents knew about their job and about magic. Skulduggery himself had written the report and delivered the sorcerer straight to his cell, as he was the only one that could get close without risking death. so, back on the main topic, Skulduggery was walking in his front door when there was a sound of something landing on his couch. it had a one-of-a-kind sound, like a child screaming as it was being torn apart...not that he actually knew what that sounded like. even lord vile had standards. he took out his gun and silently moved into the main living room. he took one look inside and stopped. there was a short skeleton with a giant grin lying on his zombie-couch. there was a long slash across its torso, which was somehow bleeding, rather heavily he would have to note. the skeleton took a look at him with the small lights in its pitch-black sockets and muttered, **"** **Papyrus, do you want anything?"** at that moment, skulduggery put away his gun, whipped out his phone and called Fletcher.

"'sup, Skul'. what do you need?" Fletcher sounded genuinely interested as to why Skulduggery would call him. normally it was either to mock him about his hair or to teleport something or someone. other than that, he never called.

"i need something teleported to the sanctuary hospital wing."

"straight to the point i see. well, first off, where are you?"

"my house, the main living room."

"this must be very urgent. did someone stomp on your favorite hat, and now you're having a panic attack?"

"just get over here."

"fine, fine..." he grumbled, then hung up. a split second later, Fletcher was standing next to Skulduggery. "okay, what is it you need me to-" he shut himself up when he saw the skeleton.

Skulduggery tilted his head at him. "i don't think i need to explain anything."

all Fletcher could say was, "that's a lot of blood."

Skulduggery nodded. "yes, yes it is. now as i said, i need you to teleport this to the sanctuary hospital wing so they don't die. this is a first for me too, now let's get this over with." Fletcher hesitantly grabbed its blue furry hoodie and, when Skulduggery was holding on, teleported straight to doctor Synecdoche's office. the doctor themselves was shocked at their sudden appearance and fell backwards in their rather comfy office chair. "that wasn't so bad, was it Fletcher?" Skulduggery cheerfully said to the teleporter.

Fletcher responded with, "i think i'm gonna be sick."

the doctor was instantly by his side with a bucket. "not in my office please." she said leading him out. once Fletcher was gone she turned to Skulduggery. "what do you want, detective? are you already in need of medical assistance after what happened this afternoon." (will be explained in the end author's note)

he tilted his head at the doctor in a manner that displayed confusion. "isn't it obvious? or did you not notice the slowly bleeding skeleton in the room that's not me." their gaze shifted downwards and her eyes widened as she finally noticed the small skeleton at his feet.

"take it straight to an operating table, it's clear this...person, will die if I don't do something soon." (yeah, we totally have time for this. JUST HEAL HIM ALREADY!)

they did just as the A/N said, without knowing. the doctor easily sealed the wound and somehow, replenished the skeleton's blood. the small skeleton's wound was near fatal. it seemed that a knife had been cut it/him right across the torso. had they waited a few more moments, the skeleton would have died (again). Skulduggery and Synecdoche watched the skeleton for a few minutes, then the doctor excused themselves, saying they had work to do. after nearly an hour, the doctor came back to check on the skeleton, which was starting to wake up. the lights in its eye sockets flickered into existence and stared at them. it was a long, awkward silence before it said something.

 **"heya. howzit goin'? why am i not dead?** **"**

 **author's note:**

 **this is the start of my other big project. i figure i'm not going to get any work done on my other story and, unlike my other story, i have motivation for this plus, this story keeps coming back to me. i know, i said i wasn't going to abandon my story, but i'm past it. when i started the other story, i was super into the creepypasta mascot Jeff the Killer and skulduggery pleasant still had the final book to look forward to, but now i'm over it. far as i'm concerned, i see where people are coming from when they say JTK sucks. not skulduggery though. if i was over that, i wouldn't be crossing over undertale with our favorite skeleton detective.**

 **on other things, the event that happened that afternoon, the murderer did some rare magic trick which severed the magic to skulduggery's head. basically, skulduggery had to walk around holding onto his head to keep it from falling off until they got it fixed. it's kinda funny to imagine. i thought about explaining how sans got through the barrier in this A/N, but turned against it. all will be explained later. all i'm gonna say is, sans isn't the only thing that got out. oh, and one more thing, it would be greatly appreciate if you could give me ideas for puns to make in the next chapter. sans making puns always makes me laugh, but i'm actually not that great at coming up with them so, you-know.**

 **hope you enjoyed the beginning and are looking forward to more chapters. reviews are welcomed. seeya on the next chapter-sceera :)**


	2. Chapter 2

**Before we get to the story I just want to say THANK YOU for the support! The amount of follows and favorites I've gotten and the awesome reviews have helped greatly. This story has gotten more love (the good kind) in the first month than my other story did in its whole existence starting last year. Then again, it's been helping my self-worth, with the thought that people like what I do, more than my motivation to write chapters. I am writing them, don't worry, and I love writing this,** **just don't expect regular chapter updates. I'll write the chapters at my own pace. Now that that's cleared up, let's get to what you came here for.**

Sans was having a great dream. It involved being the emperor of a great city where everyone had to make puns with every fifth sentence. When the dream started to fade, so did the puns that were made. He felt disappointed. He could have had a lot of fun with papyrus this timeline. It suddenly occurred to him that he never dreamed between timelines. He usually instantly woke up in his bed back in Snowdin. Instead, as the waking world faded into existence, so did two figures. One was a female human who seemed to be a doctor of sorts. The other was a...his mind raced as he saw them.

The other person was a skeleton. Unlike Papyrus or himself, they appeared to be unable to form expressions. He had to admit, they had great fashion sense, with that awesome hat and his rather nice suit. **(1)** They appeared to be in a hospital of sorts, though there were some weird things around and some very intimidating guards with scythes strapped to their backs at the exits. Despite the situation, he kept his joking demeanor and grinned up at the odd pair of individuals.

 **"Heya. Howzit goin'? Why am I not dead?"** the doctor's reaction to him speaking was hilarious. They had an incredibly shocked expression which resembled that of a startled fish. (That sounds familiar somehow) Although, he didn't know why they overreacted so much. A talking skeleton shouldn't be that surprising. Chances are the skeleton in the suit was able to talk. Maybe it was because his jaw moved like a normal mouth when he spoke. Who knows other than that god-like being observing all this?

 _Wait, what?_ He tried to recall the thought he just had but couldn't. It had vanished completely from his mind. It was probably nothing. Anyway, after the doctor regained their composure, they began to scribble something down on a clipboard. He felt the wound on his chest and winced. It still hurt, but at least he wasn't dying. Then again, even if he didn't die, the human would have reset by now, so he should be back in Snowdin, getting woken up by Papyrus.

The other skeleton shook its head in embarrassment from the doctor's actions. Unlike the doctor, the skeleton had just tilted its head curiously at him when he spoke. It opened its jaw and said "to answer your question, you're not dead because we healed you." The skeleton's voice smooth, intelligent. Experienced.

 **"Hmm. You're either my...relative, or my brother back from the dead. You can't be my relative, that's impossible. You could be my brother that came back from the dead with a quieter voice, greater intelligence and a _much_ better fashion sense. Then again, Papyrus wouldn't just change even if he came back from death. I should know. I guess you're a completely different skeleton. Or maybe...no that's impossible."** Sans banished the thought from his mind. There was no way he could do that even intentionally, so how could he possibly do it unintentionally.

"What's impossible?" The skeleton asked.

Sans thought about what answer would satisfy the skeleton's curiosity without revealing too much. He settled for a casual joke. **"Hehehe. _Tibia_ honest, it's a _skele_ -ton of work to explain and I can't be bothered."**

The skeleton chuckled at the pun. "Well, if you're going to be like that, i suppose you're going to be fine. As soon as you're able to walk, try to find me. I'll need to ask you some questions about you and where you came from. Doctor Synecdoche-" the skeleton finally noticed that the doctor had left to do some other, more important things.

- _LINE-BREAK-_ **(2)**

Over the next week, Sans recovered perfectly. well, mostly. the slash that almost killed him had healed, but there was still a long ridge across Sans' ribs which substituted a scar. he was going to be stuck with it for the rest of his life (or until the next reset he's affected by). Sans explained that he was from Mt Ebott, that something bad was happening (he wasn't specific) and that something had happened to let him through the barrier, though he wasn't sure. the skeleton with great suits and hats introduced himself as Skulduggery Pleasant, a detective, sorcerer (Sans had a problem with that, but Skul-man cleared that up by saying he wasn't around when the barrier was put in place) and dead. seriously, he was dead and had been for a long time. that was the only part of what Skulduggery was saying that caught Sans' attention until he mentioned something interesting.

oh right, i should explain. at that current time, Sans was listening to Skulduggery giving a final report of his condition before he was to be released and then interrogated a bit more. (they already know everything, so why would they do that?) shut it. they don't know everything and you're not here yet. (that's right. not _yet_. hehehe.)

"we were checking your soul for permanent damage **(3)** when we noticed something... _bonded_ to it. we're not quite sure what it is, thought it appears to be a soul of sorts. it doesn't behave like any normal human soul or like your monster soul. the magic level was off the charts." he flipped through the pages of a file, likely information on this mystery soul **(4)**. "since you seem to know more about monster souls than we do...uh...it would help if you could...uh...what are you staring at?"

Sans was staring at the faint, shadowy outline of a tall, skeletal monster standing behind Skulduggery. just as described, it was tall, and seemed to be dressed in a long black lab coat. while the upper part of it was a shadowy form, the lower part turned transparent and faded out into nothing. it's face was hard to make out, but what could be made out was large eye sockets and a wide mouth curved up into an eerie smile. he could feel it staring right back at him. it seemed to notice that Sans could see it, and seemed to wave at him. it looked around and drifted towards an injured human that was bleeding all over the place. the ghostly monster's hand drifted over the human's chest and dragged out the human's soul. the doctors surrounding the human paused and stared at the soul. it was a strong orange color, signifying bravery, but the color was fading, cracks working all across its surface. the shadow monster reached out and took hold of the dying soul using black tendrils that dropped from its fingers. the tendrils seemed to smother the soul and when they released it, the soul had turned a blank grey color and seconds later, it shattered. the monster had sucked the determination out of the soul.

the moment the soul shattered, the monster appeared to gain mass and become solid. in less than three seconds, the ghost monster was surrounded by the humans in grey with their scythes unsheathed and aimed for where the monster's throat would be. the monster's expression didn't change, it didn't even flinch at the presence of the blades. now that it was in a more physical form, Sans could fully see what it looked like. just as he thought, it was dressed in a very formal outfit, which blended in with the black lab coat and contrast with its stark white skull and hands. speaking of its hands, each had a wide hole in its center. cracks ran up, over its cranium from its right socket and down to its mouth from the left socket. in the blackness of the eye sockets, each had a small white dot, almost like a light, but not quite.

the monster held itself with confident, almost arrogant posture, standing straight and hands behind its back. it raise its left hand casually, like it had nothing to fear and it wasn't in any danger and as it did so, the hand glowed an artificial looking purple color. the soul yellow souls of the humans in grey appeared. the monster flicked its wrist and they were thrown into the walls of the medical facility.

a click sounded and the monster turned straight into the aim of Skulduggery's revolver. "don't move, or i'll pull the trigger." the monster tilted its head curiously at Skulduggery, the dots in its sockets shifting their gaze from him to the gun and back again. a spectral hand with a hole in it appeared out of nothing and grabbed the gun, forcing it out of Skulduggery's grip. another flick of its wrist and skulduggery was sent crashing into a wall. the monster turned its gaze to Sans and opened its mouth to speak, but instead of words, it emitted strange mumbling and glitching sounds. well, that's what it sounded like to Skulduggery. to Sans, it sounded like this:

 _"it's been a long time, Sans."_

 **aaand that's a cliff-hanger! hope i did a good job with this one, and my followers are still interested. okay, i'm sure you've been wondering what was with the bold numbers. they mean that i felt the need to explain something without the issue of making it fit into the story. here are the things:**

 **(1)-i'm just commenting that Skulduggery has great fashion sense and he makes it look better than most people. there will be NO shipping in this story. even if that was my intention, i suck at writing romance. i know this because I've never done it before.**

 **(2)-i couldn't think of a way to keep the conversation going.**

 **(3)-i imagine that in the time this is based in, let's say a few years after Valkyrie returns to Ireland, the sanctuary continued Nye's work of finding the soul and succeeded, and through that, they were able to learn a lot, including how to analyse it for damage. sadly, their research of the soul did not give them the ability to enhance magic at the level of the accelerator. they can increase the power of their magic, just not on the crazy level of the accelerator.**

 **(4)-how else could i describe it?**

 **that's everything! i kinda just guessed what the number 4 was about, by the time i got around to this i had forgotten what it was for. i would have updated a few days ago, but i ran out of computer time at the library. seriously, i'm using library computer time to write this since the computer i have at home is usually being used by my brothers for roblox or something. okay, how would any of you describe Gaster? we all know who he is by now, he's not a mystery any more. i figured my description could be a bit better. if my description isn't very good to you, i'll probably change the image for this story to a fan-art image of Gaster so you see what i'm imagining. there might not be another chapter for a while, since i need to figure out how i'm going to start the next chapter.**

 **i've talked enough, follow and favorite if you enjoyed it, reviews would be appreciated. oh, and speaking of reviews, just out of curiosity, what's your favorite undertale AU? stay awesome and love undertale-sceera**


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